In the area of cosmetics, there is a wide variety of cleansing cosmetics for removing makeup, including cleansing cosmetics containing large amounts of oils (oil components), such as those in the form of creams, milky lotions, oils, and oily gels; and cleansing cosmetics containing none or trace amounts of oils, such as those in the form of lotions and aqueous gels.
The cleansing cosmetics containing large amounts of oils, through having excellent detergency (cleansing power), are sticky due to residual oily ingredients even after rinsing, and thereby need another cleansing typically with a facial cleansing agent. In addition, they are not suitable for use in a bathroom, because they have poor detergency and give poor feeling upon use when the skin is wet. Independently, the cleansing cosmetics containing none or trace amounts of oils have weak detergency, although they less give sticky feeling (oily feeling) after rinsing.
To solve these problems, there have been reported aqueous gel detergents each including a polyoxyethylene fatty acid ester (see, for example, Patent Literature (PTL) 1 and 2). The aqueous gel detergents, however, not only have insufficient detergency but also suffer from a safety problem of the polyoxyethylene fatty acid ester. In addition, they have poor storage stability because of having a fatty acid moiety in the molecule.
As a possible solution to the safety problem, there have been investigated cleansing cosmetics including a polyglyceryl fatty acid ester or a polyglycerol monoalkyl ether (see, for example, PTL 3 and 4). However, the cleansing cosmetic including a polyglyceryl fatty acid ester suffers from poor temporal stability, because the polyglyceryl fatty acid ester is liable to be hydrolyzed in a system containing water (water-incorporated system). As the cleansing cosmetic including a polyglycerol monoalkyl ether, there is known a water-incorporated cleansing cosmetic, but this forms neither lamellar liquid crystal phase nor bicontinuous microemulsion and has insufficient detergency.
Recently, a technique for forming a bicontinuous microemulsion including an oily phase and an aqueous phase both being continuous has been developed by using a specific polyglyceryl fatty acid ester (PTL 5). This technique has been developed as a technique for solving the drawbacks of oily cleansing cosmetics, i.e., the problems of poor detergency and poor feeling upon use when the skin is wet. However, the polyglyceryl fatty acid ester is a complex mixture containing an unintended multisubstituted substance and a polyglycerol derivative having no hydrophobic group, thereby has a low surfactant potency, and should be added in a large amount so as to form a bicontinuous microemulsion and to exhibit sufficient detergency. This may increase irritation to the skin and may cause inflammation.